We propose to extend our work on the electrical properties of cardiac preparations. In particular, we plan to measure the properties of the individual components of cardiac tissues by determining the pathways for current flow--the equivalent circuit--of the preparation. The equivalent circuit is determined by a combined morphological, morphometric, theoretical, numerical and experimental approach: morphological, because the topology of the circuit is determined from the qualitative structure; morphometric, because the amount of each structure is determined by quantitative morphological measurements; theoretical, because theory is needed to link the morphology with the expected electrical properties; numerical, because numerical analysis of the theoretical expressions is unfortunately necessary; experimental, because electrical measurements are needed to determine the equivalent circuit. In this way we hope to determine the role of individual structures in the excitation and contraction cardiac muscle.